| Abbreviation | Definition |
|---|---|
| ATC | Applied Technology Council |
| ATCC | American Type Culture Collection |
| ATCLT | Appalachian Trail Conference Land Trust |
| ATCP | Ataxia- Telangiectasian Children's Project |
| ATCYF | Aid To Children, Youth, and Families |
| ATF | American Taekwondo Foundation |
| ATFA | American Task Force Argentina |
| ATFT | Association for Thought Field Therapy |
| ATIC | Association for Tenant Involvement and Control |
| ATME | Association of Travel Marketing Executives |
| ATNF | Apollo Telemedicine Networking Foundation |
| ATOS | American Theater Organ Society |
| ATP | Armenia Tree Project |
| ATRA | American Tort Reform Association |
| ATRA | Arizona Tax Research Association |
| ATREE | Ashoka Trust for Research in Ecology and the Environment |
| ATRI | AIDS Treatment and Research Information |
| ATRS | Air Transport Research Society |
| ATSA | American Translation Studies Association |
| ATTACH | Advanced Transeuropean Telematics Applications For Community Help |